Iterators Chain Variants Iterators An iterator permits you

Iterators & Chain Variants

Iterators § An iterator permits you to examine the elements of a data structure one at a time. § C++ iterators • Input iterator • Output iterator • Forward iterator • Bidirectional iterator • Reverse iterator

Forward Iterator Allows only forward movement through the elements of a data structure.

Forward Iterator Methods § iterator(T* the. Position) Constructs an iterator positioned at specified element § dereferencing operators * and -> § Post and pre increment and decrement operators ++ § Equality testing operators == and !=

Bidirectional Iterator Allows both forward and backward movement through the elements of a data structure.

Bidirectional Iterator Methods § iterator(T* the. Position) Constructs an iterator positioned at specified element § dereferencing operators * and -> § Post and pre increment and decrement operators ++ and – § Equality testing operators == and !=

Iterator Class 1. Assume that a forward iterator class Chain. Iterator is defined within the class Chain. 2. Assume that methods Begin() and End() are defined for Chain. 1. Begin() returns an iterator positioned at element 0 (i. e. , leftmost node) of list. 2. End() returns an iterator positioned one past last element of list (i. e. , NULL or 0).

Using An Iterator Chain<int>: : iterator x. Here = x. Begin(); Chain<int>: : iterator x. End = x. End(); for (; x. Here != x. End; x. Here++) examine( *x. Here); vs for (int i = 0; i < x. Size(); i++) examine(x. Get(i));

Merits Of An Iterator • it is often possible to implement the ++ and -- operators so that their complexity is less than that of Get. • this is true for a chain • many data structures do not have a get by index method • iterators provide a uniform way to sequence through the elements of a data structure

A Forward Iterator For Chain class Chain. Iterator { public: // some typedefs omitted // constructor comes here // dereferencing operators * & ->, pre and post // increment, and equality testing operators // come here private: Chain. Node<T> *current;

Constructor Chain. Iterator(Chain. Node<T> * start. Node = 0) {current = start. Node; }

Dereferencing Operators T& operator*() const {return current->data; } T& operator->() const {return &current->data; }

Increment Chain. Iterator& operator++() // preincrement {current = current->link; return *this; } Chain. Iterator& operator++(int) // postincrement { Chain. Iterator old = *this; current = current->link; return old; }

Equality Testing bool operator!=(const Chain. Iterator right) const {return current != right. current; } bool operator==(const Chain. Iterator right) const {return current == right. current; }

Chain With Header Node header. Node NULL a b c d e

Empty Chain With Header Node header. Node NULL

Circular List first. Node a b c d e

Doubly Linked List first. Node last. Node NULL a b c d e

Doubly Linked Circular List first. Node a b c d e

Doubly Linked Circular List With Header Node header. Node a b c d e

Empty Doubly Linked Circular List With Header Node header. Node

The STL Class list § § Linked implementation of a linear list. Doubly linked circular list with header node. Has many more methods than our Chain. Similar names and signatures.